Analyzing the uncertainty of diffusive gel-based passive samplers as tools for evaluating the averaged contamination of surface water by organic pollutants

Abstract

Agarose gel-based passive samplers are nowadays one of the most effective sampling devices able to provide a quantitative evaluation of water contamination level for a broad range of organic contaminants. These devices show significant improvements in comparison to the previous passive samplers dedicated to hydrophilic compounds because they tend to reduce the effect of hydrodynamic flow conditions on the uptake rate of compounds and thus subsequently to improve their accuracy. However, albeit their effects minimized, hydrodynamic water flow and temperature are reported as variables likely to change the uptake rate of compounds that may lead to some inaccuracy if they are not adequately taken into account. This work aims to investigate the magnitude of effects of such uncorrected variables on the bias of the deduced water contamination level. The analysis of the error structure shows that the uncertainty on the diffusivity of contaminants in agarose gel and its dependency on temperature are the most inferring factors. At 8 °C, these factors are, respectively, responsible of 34 and 33% of the squared uncertainty on the final deduced contamination level. The overall uncertainty for a single exposed passive sampler is in the order of 39% and drops to 23% if threesamplers are co-exposed (at 8 °C). Despite this uncertainty, we present results for a set of pesticides and personal care products throughout a field monitoring conducted over a 4-month period, which show the potential of passive samplers to allow assessing the temporal trend of water contamination.